量子信息交叉中心学术报告026
Title: Geometric control of collective spontaneous emission
Speaker: Saijun Wu, Fudan University (吴赛骏教授，复旦大学)
Place: RM 101，Bulg. 2，Xixi Campus (西溪校区西二楼101室)
Date and time: 14：00，Sep 4th，2019 （9月4日周三下午14：00）
Abstract：Spontaneous emission of photons is typically a decoherence effect to avoid when levels in small quantum systems are chosen to encode information for e.g., quantum computation, simulation, or sensing. On the other hand, spontaneous emission is the process for light-matter quantum information transfer. As ``spontaneous'' as it is, the information flow during the process can be controlled for photons as "flying qubits" to interconnect distant quantum objects. Major advances in quantum optics over the last twenty years provide deep understanding of such coherent light-matter interfaces and enable practical technologies for its implementations. One of most successful examples includes quantum optical memories based on collective spin excitation and superradiant Raman emission with 3-level atomic ensembles [1].
Instead of information encoding via Raman transitions, recent work [2] suggest rich physics supported by systems of dipolarly excited 2-level atomic gases. Here the long lived atomic excitation is due to subradiance: the geometry of the collective excitation ensures its weak coupling with the environment and thus suppressed spontaneous emission. Super- and sub-radiant effects have become well-known since the seminal work by Dicke in 1954 [3] on cooperative nature of spontaneous emission from ensemble of emitters. Yet general methods are still needed for precise control of collective dipolar excitations in extensive atomic medium [4], so as to access the less dissipative sub-radiant manifold, which may not only enable a class of quantum optical devices [5], but also unlock novel research regime of strongly interacting dipolar excited gases. In this talk, I will discuss a series of techniques developed at Fudan University to control collective spontaneous emissions from ensemble of cold atoms. Experimentally, by driving transition cycles in $^{87}$Rb D1 line with counter-propagating, shaped sub-nanosecond pulse pairs, we control a few-photon D2-excited $^{87}$Rb gas in its directional superradiant states, redirect the superradiance with high efficiency, and turn off the collective emission for their efficient recall later [6]. I will discuss the importance of geometric control in these recent experiments, and new research opportunities and challenges associated with the experimental technique.
[1] Luming Duan, M. D. Lukin, J. I. Cirac, and P. Zoller, Nature, 414, 413 (2001).
[2] For example: Da-Wei Wang et al, Phys. Rev. Lett. 114, 043602 (2015);
S. L. Bromley et al, Nature Comm. 7,13543 (2016);
J. Perczel et al, Phys. Rev. Lett. 119, 023603 (2017).
[3] R. H. Dicke, Phys. Rev. 93, 99 (1954).
[4] M. O. Scully, Phys. Rev. Lett., 96, 010501 (2006).
[5] For example: M. O. Scully, Phys. Rev. Lett. 115, 243602 (2015);
P. Guimond et al, Phys. Rev. Lett., 122, 93601 (2019).
[6] To be published.
吴赛骏博士简介： 2001年毕业于北京大学，获物理学士，光学硕士学位。2007年获哈佛大学应用物理博士学位，博士论文为波导原子干涉研究。2007-2011年在美国马里兰大学和国家标准技术局W. D. Phillips组从事多光子激光冷却方向的博士后研究。 2011-2014年在英国Swansea大学继续从事激光冷却方向的研究。2014年加入复旦大学物理系，研究致力于结合脉冲激光及全息显微的冷原子量子光学技术拓展。